The invention relates to an expanding head for tools for enlarging the ends of pipes and having a tool body, a mandrel which is mounted in and can be moved from the tool body and the end of which is tapered, the expanding head comprising a sleeve, which is connectible to the tool body coaxially with the mandrel and has an inwardly extending flange, and a plurality of exchangeable segmental expanding elements, which can be radially displaced in the sleeve by means of the mandrel and which are provided with flange segments, which together form an annular flange and which engage behind the sleeve flange and are all surrounded by a spring element which clamps them against each other and against the mandrel.
Tools for enlarging the ends of pipes and having exchangeable expanding heads are quite well known. In these tools, the tool body or basic tool generally includes a plurality of expanding heads, the expanding elements of which having different diameters such that their outer faces define cylindrical working surfaces. This arrangement is used to enable pipes of different diameters to be enlarged with one and the same basic tool. The companion dimensions of the connection, usually a screw-threaded connection between the expanding head and the tool body, are generally the same within a particular diameter range.
Threaded spindles, eccentrics, cams or hydraulic or pneumatic piston-and-cylinder units are used for driving the mandrel. In each case, the driving forces which are necessary for expanding the pipe and which depend upon the material and wall-thickness of the pipe and upon the transmission and friction conditions within the pipe-expanding tool, are considerable in some circumstances. The increase in the diameter of the pipe caused by the expanding operation must be at least so great that a pipe having the original diameter can be inserted into the widened portion, and in addition a sufficiently large gap must be present for accommodating soldering material introduced by capillary action. This means that the minimum increase in diameter must be greater than twice the wall-thickness of the pipe concerned.
The above-mentioned requirements render it necessary to have a relatively strong spring element for automatically retracting the expanding elements, which spring element must also have a flat characteristic curve so that no overstraining accompanied by permanent set can occur. If possible, the spring element should also be capable of returning the mandrel to its initial position so that the expanding elements can be retracted. An arrangement that has proved successful is that of fitting the spring element in an annular groove around the flange segments, since these, supported by further guide means, are responsible for the radial guiding of the expanding elements, so that the arrangement of the spring element on the flange segments makes it impossible for the expanding elements to tilt under the action of the spring since no tilting moments can occur.
U.S. Pat. No. 2,999,529 discloses an expanding head in which the expanding elements and the sleeve are interconnected by rivets which cannot, of course, be removed without being destroyed. The rivets extend, on the one hand, through the sleeve flange and, on the other hand, through the flange segments of the expanding elements, radial movement being made possible by the presence of slots in the sleeve flange. Should one of the expanding elements become unusable due to, for example, breakage, this results in troublesome repair work. In particular however, each of the expanding heads belonging to a set consists of expanding elements and a sleeve. The operator therefore has a very heavy weight to handle, since it follows that expanding heads for pipe diameters of between approximately 10 and 60 mm generally have to be carried about. Moreover, the complete expansion heads are relatively costly.
Also, German Patent Specification AS 24 59 506 discloses the idea of dispensing with rivets as the guide and fixing means and of replacing them by providing a second flange segment on the expanding elements, which second segment is disposed outside the sleeve. Thus, an annular groove, in which the sleeve flange engages, is formed between the flange segments. However, because of the overlapping necessary for ensuring reliable functioning, the expanding elements can only be removed individually one after the other from the sleeve and refitted therein. For this purpose, the spring element, in the form of a helical spring, must be removed before the expanding elements are taken out. Difficult as the removal of the spring element is, its reintroduction is even more so. To enable the spring to be fitted on the flange segments within the sleeve, it must be relatively easy to bend, i.e. "soft". Such softness does not however guarantee that the expanding elements will be held together in a reliable manner after they have been removed from the sleeve. The danger of expanding elements of different sets becoming mixed up therefore arises. Although the known system enables repairs to be carried out in a simple manner by replacing individual expanding elements, it does not meet the requirement of enabling complete sets of expanding elements to be exchanged on a routine basis and without problems when, for example, the work has to be carried out on a building site. Furthermore, the second flange segment entails a corresponding increase in the length of the expanding elements, so that there is increased bending load accompanied by the danger of fracture at the weakest place, i.e., in the floor of the annular groove. In particular, however, relatively narrow top limits are imposed upon the outside diameter of the working surfaces of the expanding element for given sleeve dimensions. Because of the difficulties associated with the operation of exchanging the sets of expanding elements, the user will bring along complete expanding heads plus sleeve.